1. Field of the Invention
The present invention concerns variable speed drive pulleys, that is to say pulleys comprising two coaxial pulley flanges in face-to-face relationship to receive a belt, constrained to rotate with a hub adapted to turn about a longitudinal axis, the distance between them being variable; at least one of them, referred to hereinafer as the mobile pulley flange, slides along the hub with radial clearance between two extreme configurations in one at least of which a primary bearing surface fast with the mobile pulley flange is brought into face-to-face relationship with a secondary bearing surface fast with the other pulley flange or wit the hub or with both if the other pulley flange is fixed, which corresponds to a frequent situation.
The invention is more particularly concerned with the risks of wear and indentation to which the aforementioned bearing surfaces are subjected in the event of rotational flexing of the mobile pulley flange relative to the hub by virtue of the aforementioned radial clearance between them.
2. Description of the prior art
The general structure of variable speed drive pulleys is well known and is summarized, for example, in U.S. Pat. No. 4,178,808 dated Dec. 18, 1979.
As is known, the mobile pulley flange is generally commanded to slide along the hub by an elastic return and rotational coupling member consisting of a diaphragm spring with variable cone angle comprising a peripheral part forming a Belleville spring in face-to-face relationship with a peripheral axial extension of the mobile pulley flange and a central part divided into radial fingers bearing against a transverse bearing member fast with the hub. More often than not the cone angle of the diaphragm spring is conditioned by the rotation speed of the pulley by means of flyweights mounted cantilever fashion on the diaphragm spring and which, by virtue of the centripetal forces to which they are subjected and which they transmit to the diaphragm spring when the latter is driven in rotation by the hub, exert on the diaphragm spring to the rotational speed of the hub.
In practice, the aforementioned mobile pulley flange oscillates between extreme configurations (generally associated with a null or minimum idling speed and a maximum speed, respectively) generally corresponding to abutment of the mobile pulley flange against the other pulley flange or a bearing surface on the hub. Between these extreme configurations at least the position of the mobile pulley flange is defined by equilibrium between the forces applied to the mobile pulley flange by the diaphragm spring and the belt by virtue of its tension.
As is known, a belt cooperates with the pulley flanges of a pulley by coming into bearing engagement with variable sectors of annular areas of the pulley flanges which because of this are subject to cyclic flexing forces tending to offset them angularly, at least, by elastic deformation: this is generally referred to as rotational flexing. In the present instance of variable speed drive pulleys, this rotational flexing phenomenon is principally reflected in cyclic tilting of the mobile pulley flange relative to the hub by virtue of the radial clearance with which it is mounted on the latter. Thus in its extreme configurations the mobile pulley flange comes into abutment against the other pulley flange or a bearing surface on the hub through variable complementary areas subject to relative movement: there result risks of wear through friction, abrasion and even indentation which may in the long term alter the performance of the pulley. Note that this rotational flexing phenomenon is significantly dependent on the aforementioned radial clearance provided for the mobile pulley flange to slide on the hub.
The present invention is directed towards alleviating these phenomena of indentation and wear by disposing between the bearing surfaces in face-to-face relationship an anti-friction member, an annular flange, for example, preferably attached to the mobile pulley flange.